Introduction to Dead Zones
By Elliot Riederer
Each year, billions of pounds of trash and other pollutants enter the oceans (National Oceanic and Atmospheric Administration, 2020). Ocean pollution is a critical issue that has serious effects on humans, animals, plants, and the environment. All life is affected by pollution, both marine and terrestrial. Human actions are the predominant cause of this destruction, as even the smallest of actions can affect the planet, and most people do not even realize the damage that results from their choices. Countless people and organizations around the world are working to raise environmental awareness, clean our planet, and prevent pollution, but it is still not enough. It takes the work of many people to make change, and more people need to be educated on the matter of ocean pollution and be inspired to take action.
People are becoming aware of the increasing amount of trash entering the oceans and it is more common for people to opt out of single-use plastics like grocery bags and plastic straws. Not using single-use products that just end up as trash is incredibly important because if humans do not stop putting trash in the oceans, all cleanup efforts will be useless. No matter how many beach cleanups people do, it will all be for nothing unless the cycle is stopped. However, there is more to ocean pollution than just the cycle of trash and discarded objects floating in the water.
An issue that affects bodies of both fresh and salt water around the world is the depletion of dissolved oxygen in the water, called hypoxia. Hypoxic waters are called Dead Zones because the number of organisms that can survive with so little oxygen is next to none. Dead Zones that are the result of human activities often get out of control and are incredibly difficult to get rid of.
Dead Zones have been plaguing our waters since the 1970’s (National Geographic, July 2020), but the problem has gained little attention and even less action is being taken to get rid of them. The world’s largest Dead Zone, in the Arabian Sea, is over 100,000 square kilometers (National Geographic, July 2020), and yet most people do not know what a Dead Zone is. I want to raise awareness about Dead Zones through my Gold Award so that more people can understand ways they can work towards shrinking the world’s Dead Zones until they are eradicated.
Dead Zones are not caused by one specific event. Nonpoint source pollution, as opposed to point source pollution, cannot be traced to one singular source. It occurs as a result of runoff: the draining of precipitation, snow melt, or irrigation water; which runs off the land into rivers, lakes, oceans, and other bodies of water. Runoff can carry pollutants from the air and land into the water. Some examples of these pollutants are excess fertilizers, herbicides and insecticides from agricultural lands and residential areas; bacteria and nutrients from livestock, pet wastes, and faulty septic systems; sediment from improperly managed construction sites, crop and forest lands, and eroding streambanks; oil, grease, and toxic chemicals from urban runoff and energy production; and acid drainage from abandoned mines (United States Environmental Protection Society, 2017).
Some places nonpoint pollution can come from are farms, livestock ranches, vehicles, septic tanks, timber harvest areas, residential areas, and irresponsible recreation. Point source pollution often has larger, more harmful impacts, but these big events like oil or chemical spills occur less often. Nonpoint source pollution occurs almost daily and builds up over time, making it extremely threatening.
One of the deadliest effects of nonpoint source pollution is algae blooms, and then in turn the creation of Dead Zones. Runoff often picks up excess fertilizers, which contain copious amounts of nitrogen and phosphorus. These nutrients are essential to plant growth, but too much of a good thing can have harmful effects on not only the immediate area, but further away as well. Overly abundant nutrients can trigger algae blooms, which are not necessarily a bad thing. Some algal blooms are beneficial to the environment. With the phytoplankton that make up the bloom being at the bottom of the food chain, all marine life depends on it. Less than 1% of algal blooms produce harmful toxins (National Oceanic and Atmospheric Administration, July 2020), but there are many other harmful effects that result from the excess algae coating the surface of the water. Algal blooms can block light from reaching organisms lower down, clog fish gills, and pollute drinking water.
More phytoplankton means drastic effects all the way up the food chain. Phytoplankton’s direct consumers experience a population inflation as a result from so much extra food. With such a drastic amount off new organisms being introduced to the environment, this also means more waste in the forms of excrement and dead carcasses. Eventually, the algae bloom will begin to die off, causing both dead phytoplankton and the bodies of its starved consumers to sink to the bottom. All of the animal waste and dead organisms that sink to the bottom provide an abundant source of food for bacteria.
Then the bacteria preform a process called decomposition, in which they break down dead organic materials. Most all decomposition processes consume oxygen, including dissolved oxygen in water (Lakes Monitoring Program, July 2020). Because there is so much food for the bacteria, they reproduce very quickly, which leads to more decomposition. This leads to less dissolved oxygen in the water, and in the worst cases, none at all. This is called a Dead Zone, because very few organisms can survive in waters with so little oxygen.
Hypoxia is the name for waters where oxygen concentrations are below two milligrams per liter (National Oceanic and Atmospheric Administration, 2020). Areas that maintain hypoxic conditions for prolonged periods of time are what we call Dead Zones. When a Dead Zone forms, anything that can swim or crawl away will do so. This can lead to a shortage of seafood for consumers, as well as the fact that fish and shrimp develop more slowly or not at all in and around the edges of dead zones. Low-oxygen conditions can also cause developmental defects. A North American study that found female Atlantic croaker fish around the Gulf of Mexico Dead Zone developing testes instead of ovaries (Ker Than, 2011). Organisms that can not escape the deadly waters, such as bottom-dwellers, snails, worms, starfish, plants, and microorganisms, will die.
Dead Zones affect all life in the wider geographical area, as not only the creatures living in the low-oxygen waters struggle or fail to survive. This can then cause food shortages for humans that regularly fish these waters, and lead to the inflation of seafood prices. Thirty percent of the Unites States’ seafood comes from the Gulf of Mexico (Gulf Coast Preservation Society, 2019). The Gulf consistently experiences the world’s second largest Dead Zone every year after the spring crop planting season. Sea birds and larger mobile animals like dolphins and whales also have to get their food from somewhere else. Habitats on the edge of the Dead Zone can experience overcrowding and food shortages as new animals enter the ecosystem after escaping the Dead Zone. The entire food chain is impacted by Dead Zones. As producers and low-level consumers die or their growth is stunted, their predators are robbed of and important nutrition source. The Baltic Sea, largely impacted by its 70,000 km Dead Zone, has lost 30% of its food energy because of hypoxia (Virginia Institute of Marine Science, July 2020).
While runoff is the major contributing factor that causes Dead Zones, the severity can also be impacted by a process called stratification which occurs in the presence of both fresh and salt water sources. Dead Zones can form in both fresh and salt water, but the presence of both in the same place can make the Dead Zone much worse. Freshwater is less dense than saltwater, and this buoyancy difference prevents them from mixing. This layering of the water is called stratification. Often when a hypoxic condition is forming, the lower level is much more affected. The bacteria on the bottom use up oxygen during decomposition, and stratification prevents oxygen from the surface from reaching the salt layer on top. Even though the ocean is always moving and mixing, stratification prevents currents from binging oxygen from the surface to lower down in the water column. Stronger winds in the right direction can help mitigate stratification, as it mixes the waters more and can lead to smaller Dead Zones.
Climate change can cause larger and more easily formed Dead Zones. A hotter climate means that water evaporates faster, and that the atmosphere can hold more water. Every 1°F increase allows 4% more water vapor to linger in the atmosphere (Climate Central, 2019). This means more rain, storms, flooding, and extreme weather. More precipitation leads to more groundwater and more runoff, which dumps nutrients, chemicals, and freshwater into the oceans. In 2019, increased rainfall led to the flooding of agricultural areas in the Midwest. That water that flooded into the Mississippi River, which in turn dumped the water and the excess nutrients it carried into the Gulf of Mexico, greatly increasing the size of the Dead Zone that year (Jenny Howard, 2019; Sarah Gibbens 2019). Warm water naturally holds less oxygen than cooler water because oxygen is less soluble under higher temperatures. Warmer water also increases the metabolism of marine creatures which increases their need for oxygen (Kitch and Lewitus, July 2020; Virginia Institute of Marine Science, July 2020).
As one leans more about Dead Zones, you discover that the factors that contribute to the creation and worsening of Dead Zones are numerous, but there are many simple things individuals can do to reduce and eventually eliminate Dead Zones. From large to small actions, all choices can have a bigger impact than what may be obvious at first glance. My goal is to teach young people how they can avoid harming our oceans, and also how they can directly help the environment recover from the damage already done.